1. Field of Invention
The present invention relates in general to reciprocating internal combustion engines of a type that is capable of varying a compression ratio during operation thereof. Particularly, the present invention relates to the reciprocating internal combustion engines of a multi-link type wherein each piston is connected to a crankshaft through a plurality of links, and more particularly to a crank mechanism of such internal combustion engines.
2. Description of Related Art
The paper xe2x80x9cMTZ Motortechnische Zeitschrift 58xe2x80x9d issued in 1997 in Germany shows in pages 706 to 711 an internal combustion engine of the above-mentioned multi-link type. In addition, Laid-open Japanese Patent Application (Tokkai) 2000-73804 shows such engine. In order to clarify the task of the present invention, a crank mechanism employed in the engine of 2000-73804 will be briefly described with reference to FIG. 16.
In FIG. 16, denoted by numeral 51 is a cylinder of the engine. A piston 3 is slidably received in the cylinder 3. An upper link 52 extends downward from a piston pin 5 of the piston 3. Denoted by numeral 56 is a lower link which is pivotally disposed on a crank pin 55 of a crankshaft 54. The crankshaft 54 comprises a plurality of paired counterweights 60. Each pair of the counterweights 60 have the crank pin 55 at diametrically opposed ends (viz., crank webs) thereof. The lower link 56 has one arm pivotally connected to a lower end of the upper link 52 through a first connecting pin 53. The lower link 56 has another arm pivotally connected to a lower end of a control link 38 through a second connecting pin 57. An upper end of the control link 38 is connected to an eccentric cam 59, so that a rotational movement of the eccentric cam 59 changes the position of the control link 38. With this changing, the top dead center (TDC) of the piston 3 changes and thus compression ratio of the engine changes.
In the crank mechanism of the publication, under operation of the engine, the paired counterweights 60 are rotated about an axis of the crankshaft 54 within a zone defined between the first and second connecting pins 53 and 57. For achieving such rotation of the counterweights 60 without inducing interference of the first and second connecting pins 53 and 58 with the counterweights 60, it is inevitably necessary to cause the lower link 56 to have an elongated and bulky structure, as shown, which however brings about a bulky structure of the entire construction of the crank mechanism. Furthermore, in the crank mechanism of the publication, due to its inevitable construction, it is difficult to provide the first and second connecting pins 53 and 57 with a satisfied bearing capacity.
It is therefore an object of the present invention to provide a crank mechanism of a reciprocating internal combustion engine of a multi-link type, which can provide the connecting pins with a satisfied bearing capacity irrespective of a compact construction of the crank mechanism.
Another object of the present invention is to provide a crank mechanism of such reciprocating internal combustion engine, which can provide the connecting pins with a satisfied bearing capacity and provide the counterweights with a satisfied inertial moment.
According to a first aspect of the present invention, there is provided a crank mechanism of a reciprocating internal combustion engine having. The crank mechanism comprises a crankshaft including paired crank webs with first end portions connected through a crank pin, and paired counterweights integral with second end portions of the paired crank webs, the paired counterweights having projected inner surfaces which protrude toward each other defining a given space therebetween, and a link mechanism including a plurality of links which are arranged to convert a reciprocating motion of the piston to a rotational motion of the crankshaft, a given one of the links being pivotally connected to other links through link connecting portions and swingably disposed on the crank pin so that upon rotation of the crankshaft, a peripheral portion of the given link passes through the given space, wherein at least one of the link connecting portions is placed within an imaginary circle which would be described as being centered about an axis of said crank pin and having a radius substantially equal to the distance between the radially innermost part of the projected inner surfaces of the paired counterweights and the center of the crank pin.
According to a second aspect of the present invention, there is provided a crank mechanism of a reciprocating internal combustion engine having a piston. The crank mechanism comprises a crankshaft including paired crank webs with first end portions connected through a crank pin, and paired counterweights integral with second end portions of the paired crank webs, the paired crank webs having mutually facing surfaces which define therebetween a given space; a link mechanism including a plurality of links which are arranged to convert a reciprocating motion of the piston to a rotational motion of the crankshaft, a given one of the links being pivotally connected to other links through link connecting portions and swingably disposed on the crank pin so that upon rotation of the crankshaft, a peripheral portion of the given link passes through the given space; and recesses respectively formed in the mutually facing surfaces of the paired crank webs, the recesses being positioned and sized to permit at least one of the link connecting portions to pass therebetween upon swinging of the given link about an axis of the crank pin.